Niridazole, a drug widely used in treating schistosomiasis, is transported intact into adult S. mansoni worms but is then converted into unknown metabolites. Because niridazole metabolism in the parasite probably relates to its mode of action, it is important to define the metabolism of this drug directly in the parasite. Specific objectives of this proposal are: (1) isolation and identification of niridazole metabolites formed by schistosomes after in vitro and in vivo culture with 14C niridazole; (2) development of methods for quantitating niridazole metabolites produced by schistosomes in infected hosts; (3) attempted identification of the specific metabolite(s) or metabolite precursors responsible for killing the adult schistosome.